Many large mobile machines such as mining trucks, locomotives, marine applications and the like have recently begun using alternative fuels, alone or in conjunction with traditional fuels, to power their engines. For example, large displacement engines may use a gaseous fuel, alone or in combination with a traditional fuel such as diesel, to operate. Because of their relatively low densities, gaseous fuels, for example, natural gas or petroleum gas, are carried onboard vehicles in liquid form. These liquids, the most common including liquefied natural gas (LNG) or liquefied petroleum gas (LPG), can be cryogenically stored in insulated tanks on the vehicles, or may alternatively be stored at an elevated pressure, for example, a pressure between 30 and 300 psi in a pressurized vessel. In either case, the stored fuel can be pumped, evaporated, expanded, or otherwise placed in a gaseous form in metered amounts and provided to fuel the engine.
To store and utilize cooled natural gas in compressed or liquefied forms onboard mobile machines, specialized storage tanks and fuel delivery systems may be required. This equipment may include a double-walled cryogenic tank and a pump for delivering the LNG or LPG to the internal combustion engine for combustion. The pumps that are typically used to deliver the LNG to the engine of the machine include pistons, which deliver the LNG to the engine. Such piston pumps, which are sometimes also referred to as cryogenic pumps, will often include a single piston that is reciprocally mounted in a cylinder bore. The piston is moved back and forth in the cylinder to draw in and then compress the gas. Power to move the piston may be provided by different means, the most common being electrical, mechanical or hydraulic power.
The cryogenic pumps used in these types of applications may be configured with a cold end and a warm end. The cold end is generally the end which does the pumping of the LNG or LPG and, as such, comes into contact with the cryogenic fluid. The warm end of the cryogenic pump generally contains many of the pump driving elements and may be exposed to atmospheric temperatures. This temperature difference between the cold end and the warm end of the cryogenic pump can create issues with respect to the design and operation of such pumps.
U.S. Pat. No. 5,797,734 (“the '734 patent”) discloses a gear type hydraulic pump that purports to be designed to pump both extremely hot fluids and extremely cold fluids. The '734 patent indicates that to avoid issues with regard to radial thermal expansion and contraction, the support housing, the inner rotor and outer rotor may be constructed of the same material and with the same thickness such that all three elements may have the same response to changes in temperature. While this arrangement may help alleviate issues caused by exposing the entire pump to different temperatures, it does not address issues caused by exposing different portions of the same pump to significantly different temperature such as with the warm end and the cold end of a cryogenic pump.